Manual open- and closed-bolt weapon fire control with automatic heat responsive override

ABSTRACT

A FIRE CONTROL SYSTEM FOR AN AUTOMTIC FIREARM CAPABLE OF BEING MANUALLY SET TO SELECTIVELY PROVIDE AUTOMATIC CLOSED-BOLT OPERTION, AUTOMATIC OPEN-BOLT OPERATION AND SEMIAUTOMATIC CLOSED-BOLT OPERTION. THE FIREARM CAN BE SET TO THESE MODES OF OPERATION BY MOVING A MODE-SELECTOR KNOB LOCATED ON THE EXTERIOR OF THE FIREARM. THE KNOB MOVES A CAM WHICH COOPERATES WITH SEARS PARTS TO SET THE MODE OF OPERATION. A HEAT SENSING DEVICE IS POSITIONED IN THE BARREL OF THE FIREARM NEAR THE FIRING CHAMBER TO SENSE THE TEMPERTURE OF THE BARREL AND WHEN THIS TEMPERATURE REACHES A POINT AT WHICH COOK-OFF OF A CARTRIDGE IS INCIPIENT A MECHANISM IS ACTUATED TO AUTOMATICALLY SWITCH THE FIREARM TO ITS AUTOMATIC OPEN-BOLT MODE OF OPERATION. THE FIREARM IS CAPABLE OF FIRING CASELESS AMMUNITION.

NOV. 9, 1971 PLUMER ETAL 3,618,455

MANUAL OPEN AND CLOSED BOLT WEAPON FIRE CONTROL WITH AUTOMATIC HEAT RESPONSIVE OVERRIDE Filed July 25, 1969 III/I5 Roy 0 P/zmer, 5 W (/aro/a' 521m? (LZZQM ATTORNEY United States Patent 3,618,455 MANUAL OPEN- AND CLOSED-BOLT WEAPON FIRE CONTROL WITH AUTOMATIC HEAT RESPONSIVE OVERRIDE Roy D. Plumer, Santa Barbara, and Harold Shrout,

Goleta, Calif., assignors to General Motors Corporation, Detroit, Mich.

Filed July 25, 1969, Ser. No. 844,926 Int. Cl. F41d 11/02, 11/20 U.S. Cl. 89-132 3 Claims ABSTRACT OF THE DISCLOSURE A fire control system for an automatic firearm capable of being manually set to selectively provide automatic closed-bolt operation, automatic open-bolt operation and semiautomatic closed-bolt operation. The firearm can be set to these modes of operation by moving a mode-selector knob located on the exterior of the firearm. The knob moves a cam which cooperates with sear parts to set the mode of operation. A heat sensing device is positioned in the barrel of the firearm near the firing chamber to sense the temperature of the barrel and when this temperature reaches a point at which cook-off of a cartridge is incipient a mechanism is actuated to automatically switch the firearm to its automatic open-bolt mode of operation. The firearm is capable of firing caseless ammunition.

The invention herein described was made in the course of work under a contract or subcontract thereunder with the Department of the Army.

This invention relates to fire control systems for firearms and more particularly to a fire control system which can be selectively set to provide a plurality of modes of operation and wherein the firearm is switched to an automatic open-bolt mode whenever the temperature of the firearm reaches a condition wherein cook-ofi? of a cartridge is incipient.

It is known in the art of firearms that after repeated and continuous firing of the weapon the temperature of the weapon may rise to a point Where a cartridge is fired due to high temperature and without being struck by the firing pin of the firearm. This condition is known as cookotf and is to be avoided for safety reasons during the use of a firearm.

It accordingly is one of the objects of this invention to provide an automatic firearm which includes means for reducing the hazards involved when a cook-off condition becomes incipient. In carrying this object forward a heat sensing device is provided which senses the temperature of the firearm and when this temperature reaches a point where cook-off of a cartridge is incipient the heat sensing device causes the firearm to be automatically switched to an automatic open-bolt mode of operation.

Another object of this invention is to provide a firearm which has a fire control system that can be selectively manually set to provide automatic closed-bolt operation, automatic open-bolt operation and semiautomatic closedbolt operation. In addition the firearm can be provided with means for automatically switching the firearm to an automatic open-bolt operation when the temperature of the firearm reaches a point where cook-off of a cartridge is incipient and regardless of the manual setting of the firearm.

In the drawings:

FIG. 1 is a view partly in section of a firearm which has a fire control system made in accordance with this invention;

FIG. 2 is a view partly in section of a part of the firearm shown in FIG. 1 and illustrating a fire control cam in a position to provide automatic closed-bolt operation of the firearm;

FIG. 3 is a view like FIG. 2 but illustrating the fire control cam in a position to provide an automatic open-bolt mode of operation for the firearm; and

FIG. 4 is a view like FIGS. 2 and 3 but illustrating the fire control cam in a position to provide a semiautomatic closed-bolt mode of operation for the firearm.

Referring now to the drawings and more particularly to FIG. 1 a firearm which takes the form of a rifle is illustrated and is generally designated by reference numeral 10. This firearm includes a receiver 12 and a barrel 14 suitably connected to the receiver. The firearm has a stock which is not illustrated and has a housing 16 which supports the trigger 18 and a plurality of sear parts forming a fire control mechanism which is to be described. The housing 16 can be a separate assembly or can be a part of the receiver body 12 insofar as the fire control aspects of this invention are concerned.

The barrel 14 has a bore '14A provided with suitable rifling, not illustrated, and this bore 14A communicates with a firing chamber 14B. The firing chamber 14B contains an obturator, which is not illustrated, that engages an end wall 20B of a reciprocable bolt designated by reference numeral 20. The obturator can take the form of a hollow cylindrical member having a section engaging the inner wall of chamber 14B and having an end section tightly engaging the wall 20B of the bolt when the bolt is closed. This arrangement is provided so that the firearm will be capable of firing so-called caseless ammunition which has no metallic case. The method of obturation forms no part of the present invention however and the fire control mechanism of this invention could be used with firearms using a case type of ammunition.

The bolt 20 carries a firing pin 22 which passes through the bolt 20 and a bolt carrier 24. The firing pin is moved forward to strike the primer of a cartridge when the end 22A of the firing pin is struck by a hammer, to be described. The bolt 20 and the bolt carrier 24 are so connected that the bolt can be rotated as the parts are reciprocated by a suitable cam slot and follower arrangement which is not illustrated to permit locking lugs 20A on the bolt to pass through slots 14C formed in the barrel. This is known as an interrupted lug-bolt locking system.

The bolt carrier 24 is slidably supported in the housing or receiver 12 and is reciprocated during operation of the firearm. The bolt carrier and bolt are reciprocated by a rod 26 having a section 28 disposed within the slot 30 formed in the bolt carrier 24. The rod is reciprocated by a suitable gas operated piston which is slidable about the barrel and urged in one direction by a spring 32. This gas operating mechanism forms no part of the present invention, it being understood however that each time a cartridge is fired the bolt will be moved toward the right to an open bolt position, in FIG. 1, against the force of the spring 32 and then returned to a closed bolt position under the control of the fire control mechanism to be described.

The barrel 14 is provided with a cylindrical bore 34, one end of which is positioned adjacent the firing chamber 14B and the bore 14A. A piston 36 is reciprocable within the bore 34 and has a piston rod 38 attached thereto which is formed with a slot 40. The rod 38 passes through an insert 42 and a chamber 44 is defined by the end of the piston and a part of the bore 34. The chamber 44 is filled with a material which expands with increasing temperature, for example mercury. It is to be understood however, that chamber 44 could contain any other type of material which expands with increasing temperature and which is capable of forcing the piston 36 downwardly or out of the bore 34, in FIG. 1, when the barrel of the rifle increases its temperature. Thus, an axially expandable bimetal would be suitable for forcing the piston out of the chamber in response to the temperature of the barrel. It will, of course, be appreciated that barrel temperature will depend upon the rate of firing of the firearm and, as will be described hereinafter, the movement .of the piston, in response to a temperature condition of the barrel, results in actuating the fire control mechanism so that the firearm is switched to the automatic open-bolt mode. Where an expandable fluid is used to actuate piston 36 a spring (not illustrated) is provided for urging the piston against the fluid.

A fire control operating rod 48 is provided which passes through the opening 40 in the piston rod 38. The rod also passes through an opening formed in a support section 50 of the barrel 14 and this rod has a spring retainer 52. A spring 54 is disposed between the part 58 and the part 52 and constantly urges or forces the rod 48 toward the left in FIG. 1. The rod 48 carries a pawl 48A which, in the position shown in FIG. 1, engages a part of the piston rod 38 to prevent the spring 54 from pushing the rod toward the left as viewed in FIG. 1. It will be appreciated, however, that as the fluid in chamber 44 expands the piston 36 and rod 38 are moved toward the insert 42 and when the piston becomes engaged with the insert 42 the pawl 48A will be released since it can slide through the opening 40 formed in the piston rod 38. The spring 54 will now move the rod 48 to the left and to a position where the pawl 48A engages the barrel extension part 50. As will be described this will cause the fire control mechanism to be switched to the automatic open-bolt mode of operation.

FIGS. 2, 3 and 4 illustrate the fire control parts of this invention and as will become apparent hereinafter the fire control mechanism can be set to provide automatic closed-bolt operation as shown in FIG. 2, automatic open-bolt operation as shown in FIG. 3 and semiautomatic closed-bolt operation as shown in FIG. 4. The term closed bolt operation, as used herein, means that the bolt is returned to a closed position when the trigger is released. The term open-bolt operation as used herein means that the bolt is set to an open bolt position whenever the trigger is released. It will of course be appreciated that as the bolt moves toward a closed position it forces a cartridge into the firing chamber from a magazine which is not illustrated and during the closed-bolt mode operation the cartridge is forced into the firing chamber and the bolt closed when the trigger is released. For open bolt operation the bolt is seared in a retracted position and no cartridge is fed into the firing chamber after the trigger is released.

Referring now to FIGS. 2-4 it is seen that the housing 16 supports pivot pins 60, 62 and 64 which are suitably supported by the housing 16. The pin 60* pivotally supports a bolt carrier sear designated by reference numeral 66. This sear is urged in a counterclockwise direction by a spring 68 which engages the sear 66 and the housing or some part fixed to the housing to urge the sear 66 counterclockwise. The trigger 18 is pivotally supported by pin 62 and is urged toward the dotted line released position shown in FIG. 4 by a spring 70. The pin 62 also rotatably supports a hammer sear 72 which is urged in a counterclockwise direction as viewed in FIG. 2 by a spring 73 located between trigger 18 and sear 72. The sear 72 has a projecting abutment portion 72A which, at times, engages the abutment or wall 74A provided by a slot formed in a hammer 74. The hammer 74 is pivotally supported by a pin 76 and is urged in a counterclockwise direction toward the firing pin head 22A by a spring 78.

In addition to the fire control parts which have been described a disconnector sear 80 is provided which is pivotally supported by rod or pin 64 and which is urged in a clockwise direction, in FIG. 2, by a spring 82.

The fire control mechanism shown in FIGS. 2 through 4 further includes a rotatable cam pin or rod 84 having a cylindrical shape and a flat cam or wall 84A. The cam pin 84 is rotatably supported by the housing 16 and is connected with a mode selector knob designated by reference numeral 86 and illustrated in FIG. 1. The mode selector knob 86 can be manually adjusted by the operator of the firearm to provide automatic open-bolt operation, automatic closed-bolt operation and semiautomatic closed-bolt operation since rotation of the selector knob 86 rotates the cam pin 84 provided with the cam surface 84A.

FIG. 2 illustrates the cam pin or rod 84 in such a position as to provide automatic closed-bolt operation for the firearm. It will be observed that in this position of the cam pin 84 the full diameter of the pin is disposed between the arms 66A and 72B of the bolt carrier sear 66 "and the hammer sear 72. The end 66B of the bolt carrier sear is now moved clockwise, from its position shown in FIG. 3, so that it cannot engage a sear abutment wall 24A formed in the bolt carrier 24. This should be contrasted to the FIG. 3 position of the bolt carrier sear 66 where the end 66B has engaged the Wall 24A formed on the bolt carrier 24 to hold the bolt carrier in an open-bolt position. With the parts, as illustrated in FIG. 2, the bolt is projected forward and a wall or sear abutment 24B formed in the bolt carrier 24 will engage the disconnector sear to pivot it counterclockwise in FIG. 2. This will cause the abutment wall 80A of the disconnector sear 80 to become disengaged from the sear abutment 74B on the hammer 74 with the result that after the bolt is closed and locked the hammer 74 is released and will move forward striking the firing pin 22A to fire a cartridge. This of course assumes that the trigger 18 has been pulled counterclockwise in FIG. 2 so that sear -wall 18A is out of the way or disengaged from sear abutment 74C formed on hammer 74. After the cartridge is fired the bolt carrier 24 is moved toward the open bolt position by the gas operating mechanism and as long as the trigger 18 is pulled to disengage sear abutment 18A from sear abutment 74C the firearm will be continuously fired due to continuous reciprocation of the bolt 24. In this regard each time the bolt is moved to the open bolt position the bolt carrier engages the hammer 74 to pivot it to a position where it is seared by sear 80. When the trigger is finally released the bolt will end up in the closed position shown in FIG. 2 and the hammer will be seared by the trigger.

If the cam selector pin 84 is moved to the automatic open-bolt position, as shown in FIG. 3, the portion 66A of the bolt carrier sear 66 engages the flat wall 84A of the cam rod or pin 84. This permits the part 66A to move closer to part 72B of scar 72 and in effect permits a counterclockwise rotation of sear 66 under the influence of spring 68. Now as the bolt carrier 24 is moved to an open bolt position by the gas operating mechanism the end 66B of sear 66 engages the sear abutment 24A of the bolt carrier to hold the bolt carrier in the open bolt position. This of course is assuming that the trigger 18 has been released so that the sear abutment wall 18A of the trigger engages the sear abutment wall 74C provided by a notch formed in the hammer 74. It thus will be apparent from an inspection of FIG. 3 that once the trigger 18 is released and the selector knob 86 in the automatic open bolt mode of operation the bolt carrier 24 will be held in the open bolt position once the trigger is released. When the trigger is pulled the part 18B of the trigger causes the part 66A and the sear 66 to rotate clockwise in FIG. 3 thereby releasing 66B from 24A and permitting the bolt carrier 24 to continuously reciprocate as long as the trigger is pulled. During the automatic open-bolt mode of operation, as shown in FIG. 3, the wall 24B on the bolt also moves the disconnector sear 80 counterclockwise, as shown in FIG. 2, to release the hammer 74 after the bolt is closed and locked. Sear abutment walls 18A and 74C are of course disengaged as long as the trigger is pulled clockwise in FIG. 3.

Referring now more particularly to FIG. 4 the cam pin 84 is now illustrated in such a position as to provide a semiautomatic closed-bolt mode of operation. In FIG. 4 the cam wall 84A now engages the part 72B of sear 72 while the cylindrical portion of the cam engages part 66A of sear 66. It can be seen that with this position of the cam pin the part 72B has moved counterclockwise from its position in FIG. 3 under the influence of a spring 73 and now the sear part 72A can engage the sear wall 74A of the hammer to hold the hammer in the position shown in FIG. 4 when the hammer is moved to this position by the bolt carrier 24. It will be further observed that the part 66B of sear 66 is in such a position that it cannot engage sear wall 24A and therefore the bolt will be moved to a closed position without impediment by sear 66. When the bolt moves to a closed position it moves the sear 80 to provide a partial release of hammer 74 and the hammer will be fully released when the trigger is pulled to disengage sear walls 18A and 74C. When the trigger 18 is released (dotted line position) in FIG. 4 the part 72C of sear 72 engages the trigger 18 so as the trigger moves to the released position it moves sear 72 with it causing 72A to become disengaged from sear abutment 74A but also causing sear abutment 18A on the trigger to engage sear abutment 74C on the hammer. This holds the hammer retracted until the trigger is pulled.

The firearm of this invention will be automatically switched to the automatic open-bolt mode of operation (FIG. 3) whenever the temperature, as sensed by the fluid in chamber 44, reaches a point where cook-off of a cartridge is incipient. As previously pointed out When this dangerous temperature exists the rod 48 is released and is moved leftwardly in FIG. 1 by the spring 54. It is seen in FIG. 1 that the rod 48 is connected with a bracket 90 which in turn is connected with a length of wire 92 which is secured to and loosely wrapped around a portion of the cam pin 84 to permit adjustment of knob 86 and pin 84. If desired tape could be used instead of wire or any other device which is capable of rotating the cam pin 84 to its FIG. 3 position whenever the rod 48 is released by the heat sensor. It therefore will be appreciated that should the temperature of the barrel reach a condition where cook-oil of a cartridge is incipient the pawl 48A is released and the spring 54, through the linkage, consisting of the rod 48 and the wire 92, moves the selector cam pin 84 to the FIG. 3 position which provides the automatic open-bolt mode of operation if the selector cam is not already in this position. In such a position the selector knob 86 is of course moved with the cam pin 84 and any attempt by the operator to shift the gun to the automatic closed-bolt or semiautomatic closed position will have no effect since once the selector knob 86 is released by the operator spring 54 will immediately switch the firearm t the automatic open-bolt mode of operation.

It is pointed out that in the FIGS. 2 and 3 positions of the selector cam pin 84 the sear part 72A cannot become engaged with sear abutment wall 74A on the hammer 74 as the trigger is pulled because the cam 84 is positioned to prevent this.

It will be apparent to those skilled in the art that it is desirable for safety reasons to provide the system that has been described in order that there will not be a cartridge in the weapon when the bolt is closed which might inadvertently fire due to the barrel reaching the cook-off temperature point.

It should be pointed out that when the heat sensor does shift the firearm to the automatic open-bolt mode of operation it is still possible to continuously fire the weapon as long as the trigger is pulled.

What is claimed is:

1. A fire control system for a firearm comprising, a firearm having a barrel provided with a firing chamber and a reciprocable bolt movable between open and closed positions, a trigger, a pivotally mounted bolt sear engageable with bolt sear abutment means and with said trigger and movable at times into engagement with said sear abutment means to hold said bolt in an open position when said bolt is shifted to an open position and when said trigger is released, a manually operable mode selector cam for adjusting the position of said bolt sear whereby said bolt sear can be pivoted out of a path traversed by said bolt sear abutment means whereby said bolt can be moved to a closed position to provide a closed-bolt mode of operation for said firearm, said selector cam being shiftable to a position where it permits said bolt sear to move to a position where it can engage said bolt sear abutment means to provide an open-bolt mode of operation, a hammer for said firearm, said hammer cooperating with a firing pin carried by said bolt, sear surfaces located respectively on said hammer and said trigger for controlling the action of said hammer, a heat sensing means in said barrel which is actuated whenever the temperature of said barrel reaches a point where cook-off of a cartridge is incipient, and means operated in response to the actuation of said heat sensing means for rotating said mode selector cam to a position wherein said bolt carrier sear is positioned to engage said bolt to provide for open-bolt operation of said firearm.

2. A fire control mechanism for a firearm comprising, a firearm having a reciprocable bolt carrier suppotring a bolt, first and second bolt sear abutments on said bolt carrier, a pivotally mounted hammer, a pivotally mounted disconnector sear having a sear abutment engageable with a first sear abutment formed on said hammer and engageable with said first bolt sear abutment on said bolt carrier to release said hammer from said disconnector sear when said bolt moves to a closed position, a piovtally mounted bolt carrier sear engageable with said second sear abutment on said bolt carrier when said bolt carrier sear is pivoted into the path of movement of said second sear abutment, a pivotally mounted hammer sear, said hammer sear having a part engageable at times with a second abutment on said hammer, a trigger, said trigger having a trigger abutment engageable with a third abutment on said hammer, a manually operable rotatable selector cam positioned between and in engagement with said hammer sear and said bolt carrier sear, said selector cam in a first position permitting said bolt carrier sear to pivot to a position where it can engage said second sear abutment on said bolt carrier while maintaining said hammer sear out of engagement with said second abutment on said hammer to provide automatic open-bolt operation, said selector cam in a second position causing said bolt carrier sear to assume a position where it is disengaged from said second bolt sear abutment and causing said hammer sear to be disengaged from said hammer to provide automatic closed-bolt operation, said selector cam in a third position permitting said hammer sear to engage said hammer while maintaining said bolt carrier sear out of the path of movement of said second sear abutment on said bolt carrier to provide semiautomatic closed-bolt operation, shiftable means connected to said selector cam, a spring for urging said shiftable means in a direction to move said selector cam to said second position to provide automatic open-bolt operation, detent means engagable with said shiftable means to maintain it in one position, and heat sensor means associated with said firearm and operable to release said detent means from said shiftable means when the temperature of said firearm reaches a predetermined value whereby said spring moves said selector cam to said automatic open-bolt mode of operation.

3. A fire control mechanism for a firearm comprising, a barrel having a chamber, a reciprocable bolt including means for closing said chamber and including a bolt sear abutment means movable along a predetermined path, a rotatable hammer engageable with a firing pin carried by said bolt and movable to a cocked position by said bolt when said bolt is opened, a pivotally mounted bolt sear including means engageable with said bolt sear abutment means for holding said bolt in an open bolt position whenever said bolt sear is pivoted to a predetermined position, a pivotally mounted hammer sear including means engageable with a part of said hammer for holding said hammer in a retracted position, a trigger, a spring interposed between said trigger and hammer sear, said trigger and hammer having cooperating engageable sear surfaces which become engaged whenever said bolt is retracted and when said trigger is in a released position, a pivotally mounted disconnector sear, said disconnector sear and hammer having engageable sear surfaces which become engaged when said bolt is retracted, said bolt including means engaging said disconnector sear to pivot it in one direction to thereby disengage said hammer and disconnector sear surfaces whenever said bolt is moved to a closed position, a manually operable mode selector cam means located between and engageable with said bolt sear and said hammer sear, said cam means in a first position providing automatic closed-bolt operation by maintaining said bolt sear and said hammer sear in predetermined positions, said cam means in a second position providing automatic open-bolt operation by causing said bolt sear to be pivoted into the path of said bolt 2 sear abutment means on said bolt, said cam means in a third position maintaining said bolt sear in a position where it cannot engage said bolt abutment means but permitting said hammer sear to engage said hammer when UNITED STATES PATENTS 2,714,334 8/1955 Harvey 89-49 X 2,858,741 11/1958 Simpson 89-140 3,045,555 7/1962 Stoner 89-142 3,446,114 5/1969 Ketterer 89140 FOREIGN PATENTS 710,250 6/1954 Great Britain 89132 BENJAMIN A. BORCHELT, Primary Examiner 0 s. c. BENTLEY, Assistant Examiner 

